Background: Attention Deficit/Hyperactivity Disorder (ADHD) is a common psychiatric problems in childhood. For teachers to achieve their roles in early detection and management they need to have good knowledge. Aim: to assess teachers' knowledge and misperceptions about ADHD among primary school students. Subjects and Methods: This descriptive cross-sectional study was carried out at primary schools in Abu Hammad city at El-Sharkia Governorate in Egypt on 235 full-time teachers. A self-administered questionnaire including a scale for Knowledge of Attention Deficit Disorder Scale was used in data collection. The fieldwork was in the second semester in the academic year 2018/2019. Results: Teachers’ age ranged between 25 and 57 years, 74.0% were females, and 78.7% from rural areas. Teachers’ satisfactory knowledge was highest for symptoms/signs and diagnosis (52.3%), while treatment was the lowest (30.2%). Overall, 30.6% of the teachers were having satisfactory total knowledge of ADHD. Teachers’ lack of knowledge about treatment was mostly regarding dietary intake of sugar or food additives (51.5%), stimulant drugs (53.6%), and Electroconvulsive Therapy (53.6%). Income and attendance of training courses were positive predictors of most knowledge areas. Conclusion and recommendations: Primary school teachers lack knowledge about ADHD. The Ministry of Education should conduct specialized in-service training courses for them to improve their knowledge. Further research is suggested to evaluate the effect of a behavioral training program for teachers to improve their knowledge about ADHD and manage ADHD symptoms in the classroom. Psychosocial intervention programs for children with ADHD and their families to strength the parent child relationship and fostering family school collaboration.